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Configuring Quality of Service 621
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Configuring Quality of Service
Quality of Service Overview
This section gives an overview of Quality of Service (QoS) and explains the QoS features available
from the Quality of Service menu page—Differentiated Services and Class of Service.
In a typical switch, each physical port consists of one or more queues for transmitting packets on the
attached network. Multiple queues per port are often provided to give preference to certain packets
over others based on user-defined criteria. When a packet is queued for transmission in a port, the
rate at which it is serviced depends on how the queue is configured and possibly the amount of
traffic present in the other queues of the port. If a delay is necessary, packets get held in the queue
until the scheduler authorizes the queue for transmission. As queues become full, packets have no
place to be held for transmission and get dropped by the switch.
QoS is a means of providing consistent, predictable data delivery by distinguishing between packets
that have strict timing requirements from those that are more tolerant of delay. Packets with strict
timing requirements are given “special treatment” in a QoS capable network. With this in mind, all
elements of the network must be QoS-capable. The presence of at least one node which is not QoS-
capable creates a deficiency in the network path and the performance of the entire packet flow is
compromised.
To display the Quality of Service menu page, click Quality of Service in the tree view. The two types
of QoS available are links on this menu page. These links are:
• Configuring Differentiated Services
•Class of Service
•Auto VoIP